Process for coating the internal surface of hydrothermosanitary pipes, particularly made of aluminium, with resinous products and pipes obtained therewith

ABSTRACT

A process is described to realize a film made of an adequate resinous material on the internal surface of metallic pipes, particularly those made of aluminium, to protect them and further allow for particular uses for which they could not be employed otherwise. These pipes are preferably applied in the hydrothermosanitary field.

The present invention deals with a process for coating the internalsurface of hydrothermosanitary pipes, particularly made of aluminium,with resinous products, also of the atoxic type or "for foods", and withthe related pipes obtained with such process.

In hydrothermosanitary plants, pipes play a role that cannot beneglected. Currently, pipes made of iron (zinc-coated pipes), of copperor resinous materials, etc. are used. Aluminium pipes, even though theycost much less, are not used, because they can be easily corroded fromthe chemical and electro-chemical (stray currents) points of view.

All metallic pipes can then be coated by limestone, depending on waterhardness and temperature. Problems deriving from limestone, chemicalcorrosions and stray currents are solved for metallic pipes, but aboveall for aluminium pipes, by adopting the protection of the internalsurface thereof, protection that can be achieved by the process claimedby the present invention.

After having carried out the pipe seal test (in coils or in rods),through pressurized air, in order to ascertain the absence of defects(due to pores or cracks), a resinous liquid is injected inside the pipe(generally kept at ambient temperature), said liquid having to wet allthe internal surface thereof. In order to enable the whole internal pipesurface to be coated by the resinous liquid flowing inside it, the pipe(generally in coils) is placed and kept slowly oscillating or slowlyrotating for all the length of the present operation and of the furtheroperations.

Afterwards, air is blown into the pipe, and the liquid is made turbolent(facilitating wetting of possible areas that had not been coated by it)and the excess liquid is removed.

Then, a gauged head, equipped with adequate gaskets (shaped as a socket,like those used for pistons, or shaped as an O-ring, etc.), is insertedand, urged by compressed air, crosses the whole pipe "shaving" theinternal surface (improving adherence of the resinous liquid on theinternal pipe surfaces) and adjusting the resinous liquid thickness andfinally exhausting the excess (of liquid) that should result from it.

Finally, the pipe (arranged in coils or in rods), still subjected tooscillation or rotation, is inserted into an oven and is subjected tohot air blow-in, to facilitate and speed up scavenging of (solvent)gases, that are removed from the resinous liquid fill that covers theinternal pipe surface.

When the protective resinous fill has been strengthened, the operationcomes to an end. A pipe is obtained with a smooth and continuos internalsurface, having resistance properties to wear, chemical andelectro-chemical corrosions and having atoxicity and anti-adherenceproperties to limestone that pertain to the adopted resinous product.Fixing of the fill to the pipe material is such that no disjunctionswhatsoever occur, neither due to thermal stresses, nor due to mechanicalstresses. The pipe therefore can, during installation, be shaped, bent,squashed without any problem and, during operation, can be subjected tonormal thermal variations to which the plant is subjected.

The process with the related described sequences, that have been adoptedfor the pipe (generally made of aluminium) wound in coils, is alsoadopted for the rod-configured pipe by carrying out the adequatemodifications required.

If the pipes in rods are horizontally arranged, the end rods areconnected with tubular fittings (such as to create a seal to theblown-in air and the passing continuity for the shaving head), so thatthey are all arranged in series, and then the procedure adopted forpipes in coils is adopted.

That is, the resinous liquid is then injected.

Afterwards, pressurized air is blown-in and the liquid is made turbolentwhile the eccess one is removed.

The shaving head is inserted and this, urged by compressed air, crossesthe whole pipe.

This operation improves liquid adherence to the internal surface, whilethe resinous liquid thickness is adjusted in adherence and the possibleexcess is exhausted. Everything is finally taken to an oven whilecontemporarily blowing-in hot air, to scavenge the solvent gases that goout of the resinous liquid film covering the internal pipe surface.Should the pipe rod arrangement be vertical, instead, the resinousliquid is made go inside the pipes by immersion. Then, the pipes arelifted and let drip. The shaving head is inserted into each pipe andmade pass therethrough, and then the pipes are taken into an oven tostrengthen their film.

In the previously-described treatments, if a thicker film has to beobtained, the cycle is repeated twice or three times.

Further, if films of a different material from the previous one have tobe overlapped when repeating the cycles, different compositions ofresinous liquids are adopted.

If in hydrothermosanitary plants, the internally treated alum/aim pipesare used and it is desirable to employ the same fittings used for theusual copper pipes, the aluminium pipes are externally coated withadequate resinous materials.

If then the metallic pipes are externally covered with suitablepolypropylene thicknesses, fittings made of thermoplastic material canbe adopted, that are already employed in these plants, carried out forpropylene pipes (Rando-type fittings).

BRIEF DESCRIPTION OF THE DRAWINGS

What has been previously described will be clarified taking into accountthe enclosed diagrammatic drawing tables, in which:

FIG. 1 is a plan view of a reel with a pipe coil;

FIG. 2 is a side view of the reel and pipe coil assembly;

FIG. 3 is a side view of an horizontal plane supporting pipes in rods;

FIG. 4 is a side view of the tanks for immersion wetting and fordripping collection of the excess resinous liquid and for the one comingfrom shaving with the adequate head;

FIG. 5 is a section of a generic pipe internally coated according to thepresent invention;

FIG. 6 is an enlarged diagrammatic view of a pipe stretch;

FIG. 7 is a side view of a generic shaving head equipped with twoflexible socket gaskets; and

FIG. 8 is a side view of the shaving head advancing inside the pipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a plan view of a reel 1 with a pipe coil 3. Reference 5 Showsthe inlet (beginning) and reference 7 the outlet (end) of the pipe.

The vessel for the resinous liquid to be injected has not been shown,nor the air source, nor the pressurized air devices nor heating sourceand apparatus. Recovery vessels and handling means, etc. have not beenshown as well. The above objects have not been represented because theirrelated means and apparatus are quite available in common productionactivities and, taken one by one and taken into account individually,cannot be considered as integral part of the inventive processdescribed.

FIG. 2 is a side view of the reel 1 and pipe coil 3 assembly. 5 and 7again show the beginning and end of the pipe 3.

A generic axis, around which the pipe coils are made oscillate or rotateduring the operating stages, has been referred to as (x--x).

FIG. 3 shows an horizontal plane 9 supporting pipes in rods 11. Thetubular fittings connecting pipe ends have been marked with 13, while 15and 17 mark the beginning and end of the assembly of pipes arranged inseries one with the other.

The tubular fittings 13 are connected to the rods 11 in such a way as tocreate a seal to blown-in air and passing continuity for the shavinghead 19, by adopting adequate measures.

In this case, too, the horizontal plane 9 supporting the pipes in rodsis made oscillate or rotate around a generic axis (y--y).

FIG. 4 shows the tanks 21, 23 for immersion wetting and for drippingcollection of the excess resinous liquid and for the one coming fromshaving with the adequate head; 25 shows the drying oven; 27 shows thechain to support and handle pipes 29. The chain 27 is equipped withconnections 31 to support pipes 29 and is periodically moving accordingto a translation motion A, coordinated with the lifting and loweringmotion B.

FIG. 5 is a section of a generic pipe internally coated according to thepresent invention and FIG. 6 is an enlarged diagrammatic view of a pipestretch.

3 shows the pipe and 33 shows the film thereof made of resinousmaterial, adhering to the internal surface thereof.

FIG. 7 shows a generic shaving head 19 equipped with two flexible socketgaskets 35.

FIG. 8 shows the shaving head 19 advancing inside the pipe 3, urged bythe compressed air, smoothing and gauging, through gaskets 35, the film33 of the resinous liquid adhering to the internal surface.

After what has been described, the relevant importance of the inventionis clarified, since it allows obtaining metallic pipes internally coatedwith resins, that, especially in the hydrothermosanitary field, are notsubjected any more to limestone deposits, and are protected againstchemical and electro-chemical corrosions in addition to those due tostray currents.

The process of the present invention particularly allows employing, inthe hydrothermosanitary field, aluminium pipes, that, being decidedlysubjected to various reaction aggressions, with respect to other metals(copper, iron, etc.), could not be used at all.

This provides a sensible economic advantage, since aluminium has areduced specific gravity and a rather low purchasing cost.

Adopting other systems, like spraying or wetting through operatingheads, applied to probes passing inside the pipes to be treated, inorder to obtain the internal protective film, is still within the scopeof the present invention.

The following are not limits to the invention: number of films (of thesame species or of different species) applied inside the pipe; nature ofmaterials composing the film (or films); thickness or single thicknessesor global thickness of the final film; colour; hardness or otherproperties.

I claim:
 1. Process for coating the internal surface of metallichydrothermosanitary pipes wound in coils or rod-configured with resinousproducts, said resinous products also being of the atoxic type which canbe used in contact with foods, characterized in that said processcomprises the steps of:injecting resinous liquid inside a pipe;blowing-in air to make said resinous liquid turbulent and to remove anexcess part of said resinous liquid; generating a film of said resinousliquid on the internal surface of said pipes; and inserting a head,equipped with flexible gaskets shaped as a ring; advancing said head,with the force of pressurized air; carrying out a shaving with saidadvancing head, said shaving including gauging and smoothing the film ofsaid resinous liquid on the internal surface of said pipe; ejectingthrough said head said excess part of said resinous liquid; stabilizingsaid film of said resinous liquid.
 2. Process for coatinghydrothermosanitary pipes according to claim 1, characterized in thatthe step of stabilizing said film includes applying heat to strengthensaid film.
 3. Process for coating hydrothermosanitary pipes according toany one of claims 1 or 2, further including the step of moving said pipeabout an axis thereof during the process, to facilitate the preventionof separations or the prevention of accumulations of resinous liquid dueto gravity and to improve wetting of the internal surface of the pipe.4. Process for coating hydrothermosanitary pipes according to claim 3,characterized in that said stabilizing step is divided into stepsof:taking into an oven said pipe; and simultaneously passing heated airinside said oven, in order to remove solvent vapors, that go out of saidresinous liquid film distributed on said internal surface.
 5. Processfor coating hydrothermosanitary pipes according to claim 2,characterized in that said stabilizing step is divided into the stepsof:taking into an oven said pipe; and simultaneously passing heated airinside said oven, in order to remove solvent vapors, that go out of saidresinous liquid film distributed on said internal surface.